G-protein coupled receptors (GPCRs) are among the most important proteins in humans because they are the 'gateway'for many signally pathways, including those that contribute to diseases, and their functions are amenable to intervention by drugs. By recognizing and binding specific chemicals, GPCRs transduce signals from the outside of cell to the inside where they trigger a cascade of biological events. Consequently, GPCRs are the most fecund class of proteins for structure determination. They are the largest class of membrane proteins;~800 GPCRs are encoded in the human genome, about half of which are potential drug targets. However, only ~60 of them are currently used as receptors for small molecule drugs and ~25 of them for bio- therapeutics based on the natural ligand;nonetheless, drugs that bind to GPCRs account for about one-third of all therapeutic drugs. The annual worldwide market for drugs that interact with GPCRs is predicted to be $118 Billion by 2014. More than 80 additional GPCRs are potentially amenable to antibody therapeutics, a novel avenue of attack that is receiving increasing attention, and one that we will explore. The difficulty in preparing samples for X-ray crystallography and Solution NMR from large membrane proteins in liquid crystalline phospholipid bilayers has been the principal roadblock to structure-based drug discovery. In order to overcome this roadblock we have simultaneously developed new methods for solid-state NMR spectroscopy and applied to structure determination of membrane proteins. Our principal target is the chemokine receptor CXCR1, and we have made substantial progress towards determining its structure during the first five years of this award. Our studies of interleukin-8 (IL-8) interacting with CXCR1 provide a framework for discovery of drugs that may affect inflammation, cancer metastasis, and other diseases by binding to CXCR1. In order to accelerate the design and discovery of drugs that interact with CXCR1 and other GPCRs, we are developing a general method for determining the three-dimensional structures of GPCRs in their native phospholipid environment under physiological conditions. This research is multidisciplinary, involving molecular biology, biochemistry, structural biology, NMR spectroscopy, and computation. It is highly effective at training scientists who can work and interact across chemical and biological boundaries. We recognize that it requires the highest levels of technology available;as a result, it is organized as a Bioengineering Research Partnership among the University of California, San Diego (UCSD) and two biotechnology companies (Cambridge Isotope Laboratories (CIL), Andover, Massachusetts and Membrane Receptor Technologies (MRT), San Diego, California. CIL's key technology is the synthesis of isotopically labeled amino acids and precursors, and the manufacture of unique isotopically labeled bacterial growth media;their effort is led by Joel Bradley, Ph.D. MRT has the technology for the expression, purification, and refolding of biologically active GPCRs developed originally by Hans Kiefer, Ph.D., at M-Fold Biotech and he remains involved in the research.

Public Health Relevance

Most diseases that afflict humans can be treated or cured with drugs. The majority of therapeutic drugs are chemicals targeted to protein receptors that reside in cell membranes, the largest class of which is G-protein coupled receptors (GPCRs). Determining the structures of GPCRs is a very high priority goal of biomedical research because it will accelerate the discovery of new drugs to treat a wide range of diseases. The research project described in this proposal will advance the method of NMR spectroscopy so that it can be used to determine the structures of GPCRs in their native environment of phospholipid bilayers under physiological conditions. This is a technically demanding project that requires the methods of chemistry, physics, and biology. This project is focused on the chemokine receptor CXCR1 and its interactions with its natural ligand interleukin-8 (IL-8) as an example that affects several diseases, including inflammatory disease and cancer metastasis. The methods demonstrated with this example should be applicable to many other GPCRs (and diseases) as well as other classes of membrane proteins.